Astronomers have spotted a moon orbiting the newly discovered tenth planet, 2003 UB313, or Xena, as it has been codenamed after the TV warrior princess. The moon, dubbed Gabrielle for the TV Xena's sidekick, is estimated to be one tenth the size of the planet, which itself is believed to measure around 2,700 kilometers across. Scientists plan to observe Gabrielle again in November and December using the Hubble Space Telescope, which should enable them to ascertain the moon's orbit and mass.